The Australian international's new deal comes as a massive boost as Simon Grayson's squad head off for the pre-season tour of Scotland today.
The former Leicester City centre-back enjoyed a clean sweep at the club's Player of the Year awards in 2010, but was sidelined for almost 14 months following an Achilles injury.
The 30-year-old Kisnorbo played the final 10 minutes of last season, coming off the bench in the 2-1 win at Queens Park Rangers, and continued his rehab over the summer before returning to pre-season training with United last week.
Grayson said: "We're delighted to get things finalised with Paddy. He's had a tough time, but we know what he is all about and what he brings to the team. He is a very important member of our squad.
"The deal shows the commitment of both the club and Paddy and it's great to have him back with everyone after being out for so long."